The determination of analyte concentrations in physiological samples plays a prominent role in diagnosis and therapy of a variety of diseases. Analytes of interest include among others glucose, cholesterol, free fatty acids, triglycerides, proteins, ketones, phenylalanine, enzymes, antibodies, or peptides in blood, plasma, urine or saliva.
Measuring the glucose concentration in samples of whole blood is a particularly common task. Since Diabetes causes dangerous physiological complications leading to the loss of vision, kidney failure and other serious medical consequences. Only a stringent therapy and disease management minimises the risk of these consequences with adjustments on exercise, diet, and medication. Some patients have to test their blood glucose concentration frequently with three or more measurements a day. These patients as well as clinicians and hospitals require an accurate, reliable, and ideally inexpensive method to adjust their treatment regimes to avoid the long-term complications of diabetes mellitus.
The increased awareness about diabetes, the acceptance of self-monitoring and self-treatment have been dependent upon the availability of suitable devices and let to the development of a multitude of devices and methods for personal use and point of care testing as well. Available are pregnancy, ovulations, blood coagulation, ketone and cholesterol tests, as example for a non-exhaustive selection, but most prominent in the area of self-monitoring is still the detection of glucose in capillary blood.
Typically, a physiological sample fluid, e. g. capillary blood, is applied to a test strip to evaluate the concentration of an analyte. The test strips are usually used in conjunction with a measuring device which measures light reflectance and/or transmittance, if the strip is designed for photometric detection, or some electrical properties, such as electrical current, if the strip is designed for detection of an electro-active compound.
Over the last couple of years electrochemical biosensors became more and more prominent on the diagnostic market and provide the patient with several advantages over the reflectance photometry systems. Main differences are the capillary fill features of the test strips allowing an easier sample application in comparison of the top fill membrane based reflectance photometry systems. Additionally, the measurement cell can be located at the tip of the strip thus the blood sample will not be in direct contact with the measurement device (meter) during the test procedure, which keeps the device clean and hygienic avoiding blood contamination of the meter.
Until today a wide variety of electrochemical biosensor strips has evolved. An exemplary electrochemical biosensor as disclosed in U.S. Pat. No. 5,288,636, includes a working and a counter/reference electrode. A reagent, which includes an enzyme capable of catalyzing a reaction involving a substrate for the enzyme, a redox mediator capable of transferring electrons transferred between the enzyme and the working electrode, and a buffer, is located at the working electrode surface. When a sample fluid containing the analyte to be measured is added to the reagent, a reaction occurs that oxidizes the analyte and reduces the redox mediator. After or during this reaction, an electric potential difference is applied between the electrodes. The current produced by the electrooxidation of the reduced form of the mediator is measured and correlated to the amount of the analyte in the sample.
In a typical embodiment, the electrochemical system consists of two electrodes on a support member enclosed by supporting walls to form a cavity which is either small enough to be filled by capillary action (U.S. Pat. No. 4,900,424; Birth et al., 1987), or with help of a spreading or mesh layers (U.S. Pat. No. 5,628,890; Carter et al., 1997).
Due to the raw material and process variations in large-scale manufacture of the analyte strips an adequate strip-to-strip reproducibility from one batch to the next is not guaranteed. Therefore, all known systems require test strips, which have to be calibrated during the production process. This calibration information is provided by the time of use to the meter by manual or automatic means. In the first case the user has to enter the calibration information in form of a number with comes with each lot of test strips, in the second case the information is encoded in the strip either by bar, colour, or a digital coding feature. Therefore this type of calibration information represents the functional characteristic of the test strip by the time of production, which may or may not be different for the test strip characteristics by the time of use that could be up to two years later.
Furthermore, the measuring procedure may be impaired by other variable factors in the physiological sample fluid. A typical complication in whole blood analysis is the variability of erythrocyte levels, leading to results which may not reflect the real analyte concentration of the sample.
PCT/EP 2004002284 discloses a dry reagent test strip for the photometric detection and quantitative determination of an analyte in a physiological fluid which is provided with an integrated calibration system using the standard addition method.
However, up to now no analyte test system exists, which is suitable for electrochemical detection and quantitative determination of an analyte in a physiological fluid and which is provided with integrated calibration and quality control means.
Therefore, it is the object of the present invention, to provide an analyte test system with an integrated calibration means, which accounts for and compensates any variability may it be generated by fluctuations in the production process or by the variability of the analysed sample itself, which has electrochemical detection means for measuring the concentration of an analyte in a physiological fluid sample.
It is a further object of the present invention, to provide a production process for the electrochemical analyte test element which does not involve many and complicated production steps and therefore is inexpensive and usable for products assisting patients in self-monitoring blood glucose or other important physiological parameters.